1. Technical Field
The present invention relates to a method of processing a silicon wafer including a plurality of silicon substrates and a method of manufacturing a liquid ejecting head that ejects liquid droplets, and more particularly, to a method of manufacturing an ink jet recording head that discharges ink droplets as liquid droplets, using a silicon wafer.
2. Related Art
For example, liquid ejecting heads have been proposed which apply pressure to liquid contained in pressure generating chambers using pressure generating units, such as piezo-electric elements, to discharge liquid droplets from nozzles. A representative example of the liquid ejecting heads is an ink jet recording head that discharges ink droplets as the liquid droplets. As the ink jet recording head, the following one has been proposed: pressure generating units, such as piezo-electric elements, are formed on one surface of a passage forming substrate having pressure generating chambers formed therein; and a nozzle plate having nozzles provided therein is bonded to the other surface of the passage forming substrate.
The passage forming substrate forming the ink jet recording head is composed of, for example, a silicon monocrystal substrate having a (110) plane as its one surface. The passage forming substrate is manufactured as follows: a plurality of passage forming substrates are integrally formed on the silicon wafer; and the silicon wafer is divided into individual passage forming substrates.
For example, as a method of dividing the silicon wafer, the following has been proposed: a break pattern having a plurality of through holes arranged at predetermined intervals is formed on cut lines between a plurality of passage forming substrates (silicon substrates) that are formed on a silicon wafer; and the silicon wafer is divided along the break pattern (for example, see Japanese Unexamined Patent Application Publication No. 2006-175668). As described in Japanese Unexamined Patent Application Publication No. 2006-175668, regions in the vicinity of the break pattern in the silicon wafer are partially etched in the thickness direction of the silicon wafer, thereby forming thin portions that have a smaller thickness than other portions.
When the silicon wafer is etched to form the thin portions, a residual portion including a (111) plane that is inclined with respect to the surface of the silicon wafer is formed in each of the through holes forming the break pattern. Specifically, each of the through holes includes a first (111) plane that is perpendicular to the (110) plane of the silicon wafer, a second (111) plane that is opposite to the first (111) plane, a third (111) plane that is perpendicular to the (110) plane and intersects the first (111) plane at an acute angle, and a fourth (111) plane that is opposite to the third (111) plane, is perpendicular to the (110) plane, and intersects the second (111) plane at an acute angle. The residual portions are formed on acute portions of each of the through holes, that is, an angular portion where the first (111) plane and the third (111) plane intersect with each other and an angular portion where the second (111) plane and the fourth (111) plane intersect with each other.
Japanese Unexamined Patent Application Publication No. 2006-175668 discloses a technique for intentionally leaving the residual portions on the acute portions when the through holes are formed in the silicon wafer, thereby reinforcing the break pattern.
Such residual portions are formed when thin portions are formed as well as when the through holes are formed. For example, even when the residual portions are not formed during a process of forming the through holes, the formation of the thin portions causes the residual portions to be formed in the acute portions.
The residual portions lower the breakability of the silicon wafer, and the presence of the residual portions causes unstable cut lines. For this reason, it is not always advantageous to remain the residual portions, but it is necessary to form the through holes without the residual portions according to various conditions, such as the thickness of the silicon wafer.
These problems occur when a silicon wafer is divided into a plurality of silicon substrates as well as in a method of manufacturing liquid ejecting heads, such as ink jet recording heads.